The long term goal of the proposed research is to identify and develop molecular genetic markers for the identification and assessment of vector competence of Ixodes spp. ticks. Ticks in the genus Ixodes (~240 spp), and especially those in the largest subgenus Ixodes (~75 spp), are becoming increasingly familiar to the public health community because of their ability to transmit multiple diseases to humans and animals, such as protozoa (e.g., Babesia), viruses (e.g., tick-borne encephalitis), and bacteria (e.g., Erlichia and the Lyme disease agent, Borrelia burgdorferi). Although only about 10% of tick species are of public health importance, it is necessary to accurately identify all species because of their different abilities to transmit disease agents, as is the case with Ixodes spp. For example, it is difficult to distinguish members of this genus when individuals become damaged upon removal, which is too often true when ticks are submitted for identification. Therefore, the specific aims of this proposal are to (1) develop a pcr-based key to all 34 species of Ixodes found in the USA using the proven segment of nuclear ribosomal DNA, the second internal transcribed spacer (ITS-2), (2) develop new polymorphic molecular genetic markers from single copy nuclear genes and introns (e.g., beta tubulin and ef-1 alpha) and by using proven RAPD primers, single-strand polymorphisms, and other techniques for identifying multiple markers in the 300-500 bp range, optimal for SSCP. In this aim, tick cell cultures will be utilized as a source of consistent and high-quality DNA, and (3) compare the vector competence of the 18 mitochondrial haplotypes of Ixodes scapularis to I. (I.) pacificus and I. (Ixodiopsis) woodi using 3 B. burgdorferi strains from the northeastern, southeastern, and western regions of the USA.